The present invention relates to an electroplating bath for the deposition of white palladium metal on various surfaces. More particularly, the invention is concerned with baths for producing thin deposits of white palladium metal.
As is known in the art, the use of conventional palladium baths produces deposits which are grey in color. There are rhodium baths, on the other hand, known to produce white deposits which are very useful in the decorative art industries. In view of the relatively high cost of rhodium as compared to palladium, it would be desirable to be able to obtain a white finish from palladium baths as a substitute for the rhodium finishes now being employed. Previous attempts to produce a white palladium metal deposit were unsuccessful because the deposit was not white enough for the intended purposes, e.g., as a substitute for the conventional white rhodium deposits. It would also be useful for commercial purposes to be able to obtain readily thin, white deposits of palladium metal.
U.S. Pat. No. 330,149 which issued to Pilet et al. 1885, does mention the production of a "white palladium deposit". The electroplating bath of Pitel et al. contained palladium chloride, ammonium phosphate, sodium phosphate or ammonia, and, optionally, benzoic acid. The operating pH of the bath is not disclosed, although it is stated that ammonia is "boiled" off and "the liquid which was alkaline, becomes slightly acid". As indicated, the use of benzoic acid is disclosed to be optional, but the patentees disclose that it bleaches the deposit and makes the deposit more striking on iron and steel.
Electroplating baths designed to improve the brightness of palladium or palladium alloy deposits on metal substrates are also known in the art. See, for example, U.S. Pat. No. 4,098,656, which issued to Deuber in 1978. In this patent the improved brightness is achieved by utilizing in the bath both a Class I and a Class II organic brightener and an adjusted pH range of from 4.5 to 12.